1. Field of the Invention
The present invention relates to a positive resist composition which is sensitized against a radiation such as a ultraviolet ray to provide a positive pattern, and is suitable to be used for production of a semiconductor.
2. Description of the Related Art
A positive resist comprising a novolak resin as an alkali-soluble component and a quinonediazide compound as a radiation sensitive component gives a positive image by irradiation of a radiation through a mask (so-called patterning light exposure) and alkali developing, i.e. utilizing a phenomenon wherein the quinonediazide compound is decomposed by the action of the radiation to generate a carboxyl group and the quinonediazide compound turns from alkali-insoluble to alkali-soluble. Such a novolak/quinonediazide type positive resist is often used in production of an integrated circuit since it generally provides for good resolution.
Recently, production of an integrated circuit has required submicron pattern forming, with the progress of higher integration which requires more minute circuits. As a result, there is required a positive resist having not only good resolution but also good focus depth. Improvement of resolution can be attained by increasing the amount of radiation sensitive component. However, increase of the amount of radiation sensitive component causes radiation absorption of the resist increase and often causes film thickness reduction when being out of focus. Therefore, it has been difficult to improve resolution and focus depth simultaneously.
Good profile (pattern form) is also required for a positive resist. That is, for a pattern becoming more minute, round shape of the top surface of a pattern and a slope between the top and the bottom of a pattern have caused such problems that the pattern of the mask used in the light exposure can not be accurately transcribed onto the pattern formed by the resist. Therefore, there is required a positive resist composition which improves these defects and provides good profile.
Profile can be improved easily by enhancing transparency of a resist, specifically, by reducing the amount of a radiation sensitive component. However, when reducing the amount of a radiation sensitive component, resolution generally decreases. Profile can also be improved by enhancing the hydrophobicity of a novolak resin. However, when the hydrophobicity of a novolak resin is enhanced, the sensitivity of the resist generally decreases. In this way, it has been difficult to improve profile without lowering sensitivity and resolution.